The present invention relates to an antenna with feed horn and polarization feed for combining or separating two linearly polarized electromagnetic waves. The antenna is of the directional or focusing variety with parabolic reflector and includes a tubular member being provided with a feed horn facing the reflector with a widening opening; further included are two wave guides connected to the above mentioned tube and separately guiding the two electromagnetic waves while being provided with differently wide dimensions in the respective plane of polarization and the respective plane transversely thereto, the connection being such that these two wave guides are disposed one behind the other in a plane with reference to the reflector. Moreover, one of the wave guides is connected with its front end in radial direction to the tubular member such that the wide side of that particular wave guide extends in the direction of the axis of the tubular member; moreover a short circuiting element is provided in the interior of the tubular member between the connection to the first mentioned wave guide and the end of the tube facing away from the feed horn.
Directional antennas of the type to which the invention pertains serve the wireless transmission of electromagnetic waves from one location to another one. They are used, for example, for the radio linking systems; communication links with satellites; radio location and direction finding equipment and etc. They should be provided with a very high degree of efficiency, simply in order to obtain a large effective distance and range. Accordingly, directional antennas of the type to which the invention pertains are equipped with energizing means which insure a high attenuation of side lobes, particularly in parasitic directions, and also are provided with a high degree of matching and overall gain. The energizing device or the antenna is usually equipped with a feed horn being arranged in the focus of a parabolic antenna which, unfortunately, entails a shading effect provided by the feed line that leads to the feed horn. These feed lines are usually electromagnetic wave guide. Their physical presence constitutes a certain shading effect which in a detrimental fashion interferes with the radiating characteristics of the antenna. The aforementioned drawbacks will, in fact, be even more noticeable if the antenna is used for two, basically separate electromagnetic waves which are either concurrently broadcasted or received or wherein one is transmitted and the other one is received. These two different waves are differently polarized and it is therefore customary to provide a polarization feed ahead of the feed horn into which the two feed lines feed; these two lines run the respective waves separately to the antenna. This double feeding, of course, provides an additional shading for the antenna.
U.S. Pat. No. 3,864,688 describes basically a polarization feed of the type outlined above, and it proposes to keep the shading effect as small as possible by connecting the two wave guides to the tubular input of the feed horn in the same plane. Therefore, these two wave guides can be run in a single plane, one behind another. However, it was found that such a mode of connection is disadvantaged by the fact that separating the two electromagnetic waves requires a considerable effort as far as the construction of the tubular feed element for the feed horn is concerned, which has to be made with a high degree of precision because one wave has to be turned by 90.degree. without interfering with the other wave and without incurring reflection. This particular objective is obtained in the equipment as per the U.S. patent by means of pins or a twisted sheet metal strip arranged in the tube between the two feed points, whereby the pins, if used, are azimuthally displaced.